1. Field of the Invention
This invention relates to organic synthesis, and more particularly to the use of certain organo zirconium complexes to functionalize olefins.
2. Description of the Prior Art
It has recently been discovered that zirconium chlorohydrides having the formula ##STR3## wherein Cp is an unsubstituted .pi.-cyclopentadienyl radical, are useful in functionalizing, at a selective position, a variety of unsaturated organic molecules. Particularly related to this invention is the use of these zirconium compounds for selective functionalization of olefins, which is defined herein as the insertion of a radical in the olefin at a particular position with an accompanying elimination of the olefin double bond.
It has been reported that the above-identified zirconium chlorohydride reacts with the olefin rapidly under mild conditions (e.g., 25.degree.-40.degree. C. in benzene) to produce a di(.pi.-cyclopentadienyl)(chloro)alkyl zirconium complex in which the zirconium is bound to the alkyl moiety at a position corresponding to the sterically least hindered position of the olefin as a whole. Reaction of the thus formed alkyl zirconium complex with an electrophilic reagent such as Br.sub.2, I.sub.2 or C.sub.6 H.sub.6 ICl.sub.2 results in cleavage of the Zr-alkyl bond and formation of the corresponding halogenated alkane. Alternatively, procedures are described for first inserting a C=O radical into the Zr-alkyl bond of the alkyl zirconium complex and then using a similar electrophilic reagent to cleave the Zr-acyl bond and prepare an alkane having an acyl halide substituent. These procedures have been found to be particularly useful in preparing .alpha.-substituted alkanes from internal olefins. Illustrations of such uses of a di(.pi.-cyclopentadienyl) zirconium chlorohydride have been published by J. Schwartz and others in J. Amer. Chem. Soc. at 96, 8115-16 (1974) and 97, 228-30 and 679-80 (1975) and in Angew. Chem. Int. Ed. Engl. at 15, No. 6, 333-40 (1976).
In the above-described procedure, various electrophilic reagents disclosed as useful in the step to cleave the Zr-alkyl or Zr-acyl bond are complex and expensive compounds and thus have questionable commercial economics. N-bromo-succinimide, N-chloro-succinimide and iodobenzene dichloride are examples of such compounds. It is desirable, therefore, to provide new and more economical methods to carry out this cleavage step. It is the primary object of the present invention to provide a new and improved method for cleavage of the Zr-acyl bond in the above-described process.
Further objects, aspects and advantages of this invention will be apparent from the description and claims which follow.